The present invention relates to magnetic domain wall shift registers, and more specifically, to systems and methods for pinning magnetic domain walls in a magnetic domain wall shift register memory device.
In a magnetic domain wall shift register memory device, domain walls are shifted along a nanowire by applying a time-dependent shift current. This shifting operation is necessary in order to read out the magnetization direction of the domains of the magnetic nanowire that are separated by domain walls. For this type of device, domain walls must be fixed in place when not shifting, but move coherently with all domain walls moving in concert when shifting. This is greatly aided by having specific pinning sites where the domain walls automatically settle and remain after the shift current is applied. A variety of suggestions for implementing such pinning sites have been made, but many (e.g., using geometric constrictions of the nanowire), result in pinning that is too strong, necessitating a large shift current magnitude. Furthermore, pinning that uses geometric constrictions as well as several other proposed methods (e.g., that utilize magnetic structures external to the nanowire), have a pinning strength that is constant in time, referred to here as “static pinning” Static pinning introduces a very significant design tradeoff between pinning that is too strong, necessitating a large shift current, and pinning that is too weak, which may lead to higher bit error rates.